#倒计时

data() {
	// vue 定义默认数据
	return {
		isStart: false,
		isEnd: false,
		d: 0,
		h: 0,
		m: 0,
		s: 0,
		timer: null,
		btnInfo: ""
	};
},

// 倒计时
countdown() {
	// 清除定时器
	clearTimeout(this.timer);
	const nowTime = new Date().getTime(),
		start = "开始时间",
		end = "结束时间";
	let startTime = new Date(start).getTime(),
		endTime = new Date(end).getTime();

	// 时间差
	let diff = startTime - nowTime;
	if (diff <= 0) {
		this.isStart = true;
		if (endTime - nowTime <= 0) {
			this.isStart = false;
			this.isEnd = true;
		} else {
			this.timer = setTimeout(this.countdown, 30000);
		}
		return;
	} else {
		// 动态计算 天、小时、分钟、秒
		this.d = Math.floor(diff / 36e5 / 24);
		this.h = Math.floor((diff / 36e5) % 24);
		this.m = Math.floor((diff / 6e4) % 60);
		this.s = Math.floor((diff / 1000) % 60);

		// 递归调用
		this.timer = setTimeout(this.countdown, 1000);
	}
}

// 活动开始时间
const start = "2020/03/16 21:31:00";

// 倒计时函数（传参数）
function countDown(start) {
    // 清除定时器
    !!timer && clearTimeout(timer);

    // 获取时间毫秒数
    let begin = new Date(start).getTime(),
        now = new Date().getTime();

    // 判断当前时间小于开始时间
    if (now < begin) {
        // 计算时间差
        let cha = begin - now;

        // 获取 天时分秒
        let day = Math.floor(cha / 36e5 / 24),
            hour = Math.floor((cha / 36e5) % 24),
            minute = Math.floor((cha / 6e4) % 60),
            second = Math.floor((cha / 1000) % 60);

        // 拼接字符串
        let timeSting = "";
        !!day && (timeSting += day + "天");
        !!hour && (timeSting += hour + "时");
        !!minute && (timeSting += minute + "分");
        timeSting += second + "秒";

        // 打印字符串
        console.log(timeSting);

        // 调用封装的倒计时函数
        timer = setTimeout(() => {
            countDown(activeStart);
        }, 1000);
    }
}
// 调用计时器
countDown(start);

countDown(time) {
	if (time == 0) {
		this.isLive = true;
		this.timer && clearTimeout(this.timer);
		this.timeString = "";
		return;
	}
	const addZero = n => (n < 10 ? "0" + n : n);
	const checkTime = (n, type) => (n ? n + type : "");
	let diff = time - 1;
	let d = Math.floor(diff / 3600 / 24),
		h = Math.floor((diff / 3600) % 24),
		m = Math.floor((diff / 60) % 60),
		s = Math.floor(diff % 60);
	d = addZero(d);
	h = addZero(h);
	m = addZero(m);
	s = addZero(s);
	d = d === "00" ? 0 : d;
	if (h === "00") h = d === 0 ? 0 : h;
	if (m === "00") m = d === 0 && h === 0 ? 0 : m;
	let _d = checkTime(d, "天"),
		_h = checkTime(h, "时"),
		_m = checkTime(m, "分");
	this.timeString = `距开始${_d}${_h}${_m}${s + "秒"}`;
	// 递归调用
	this.timer = setTimeout(() => {
		this.countDown(diff);
	}, 1000);
}
// 调用函数：时间差 number 类型数据
this.countDown('时间差')